The planting of corn, soybeans, and other crops is typically performed by driving a tractor through the field pulling a toolbar implement. The toolbar implement consists of a frame supported by wheels or tracks and having a transverse bar to which multiple planting units are attached. The planting units are spaced apart along the transverse bar to correspond to the seed rows that will be planted. The term “toolbar” is used interchangeably in the industry to refer to the implement as a whole and to the transverse bar specifically. As used herein, the term “toolbar” refers specifically to the transverse bar to which the planting units are attached and the term “toolbar implement” refers to the implement as a whole.
Toolbar implements commonly contain toolbars having widths of twenty feet (which can accommodate eight planting units spaced thirty inches apart), thirty feet (which can accommodate twelve planting units spaced thirty inches apart), and more. The toolbars are so wide that they commonly are hinged so that the overall width of the implement can be reduced for storage and for travel upon public roads.
Toolbar implements are also used in other farming operations. For example, multi-functional row units are often attached to the toolbar implement to simultaneously till (also known as cultivate or plow), plant, and fertilize in one pass through the field. This method of farming is known as strip tillage, zone tillage, or strip till farming. As used herein, the term “row unit” refers to any type of planter, tiller, multi-functional unit, or the like that is attached to a toolbar implement.
Toolbar implements typically have two positions, a lower working position and an upper storage position. In the working position, the toolbar is in a lower position and the row units are in contact with the ground. In the storage position, the toolbar is in a raised, upper position and the row units are elevated off the ground. The storage position is also used when the toolbar implement is transported.
A typical wheeled toolbar implement contains a main longitudinal frame having a connector at the front and a hitch at the rear. The toolbar is divided into three sections, a hinged left wing, a fixed center, and a hinged right wing. Spaced apart on the center toolbar are two, four, or more wheel assemblies. Each wheel assembly contains a bracket, a motion dampener, a lift arm, and a wheel. Row units are attached to the center toolbar in the spaces between the wheel assemblies.
While wheeled toolbar implements are more common, toolbar implements containing track assemblies are becoming more popular. A track assembly for a toolbar implement is described in Rosenboom, U.S. Pat. No. 7,726,749, Jun. 1, 2010, which is incorporated by reference. Track assemblies make contact with the ground with larger surface areas (footprints) and therefore reduce soil compaction and improve the ability to operate in wet fields. One disadvantage of track assemblies on toolbar implements is that turning is more difficult, both in the field and during transport, because of the larger footprints. Another disadvantage is that many toolbar implements do not keep the lower (ground-contacting) sections of the track perfectly parallel to the ground when on a side incline. Maintaining the track assemblies parallel to the ground at all times is required for optimal stability and traction.
Accordingly, there is a demand for an improved toolbar implement. More particularly, there is a demand for a toolbar implement having tracks that steer and remain parallel to the ground.